This invention relates generally to the handling of materials in vehicle beds and more particularly to apparatus which operates to unload a wide variety of materials from the cargo areas of vehicles such as pickup trucks and trailers.
Among the types of materials that are commonly carried in the cargo area of a pickup truck are granular materials such as sand, gravel, dirt and grain; building materials such as lumber, drywall panels, siding panels, bricks, stone and roofing materials; containers such as boxes, drums and cartons; waste materials such as brush, tree trimmings, scrap, tires and demolition debris; machinery such as air compressors and other relatively heavy pieces of equipment; and miscellaneous objects such as firewood, animal feed, hay bales, tools and other items. In many cases, unloading of the truck bed is a difficult and time consuming activity. For example, unloading of sand, gravel or dirt with a shovel can take a considerable amount of time and require substantial physical labor. Heavier objects are also difficult to unload, particularly those that are carried in the front end of the cargo area near the cab and must be moved to the tailgate area before they can be unloaded.
These problems have been recognized, and attempts have been made to develop equipment to facilitate the unloading of vehicle beds, as exemplified by U.S. Pat. No. 3,978,996 to Oltrogge. However, the unloading devices that have been proposed in the past have been less than satisfactory in a number of respects. Devices which are permanently mounted in the truck bed are impractical because they occupy significant parts of the cargo area and thus reduce its cargo carrying capacity and obstruct access to the truck bed. Devices of the type shown in the Oltrogge patent apply heavy loads to the relatively weak tailgate which can bend the tailgate, break its hinge or cause other damage. It is not desirable to attach the add on equpment directly to the tailgate because it is sometimes necessary or desirable to remove the tailgate.
The unloading device shown in the aforementioned Oltrogge patent is also characterized by structural weakness and the inability to handle heavy loads. Another problem is that mud and other debris can build up on the conveying belt and cause it to wind up unevenly on its roller. The build up of foreign matter on the belt can also create an uneven roll diameter which can result in the uneven application of tension, thereby unduly stressing some areas of the belt and possibly tearing or otherwise damaging or excessively wearing the belt. Hand cranking is an additional drawback because at some positions of the crank, leverage is lacking and the body weight cannot be used to good advantage.